Engineering / Wear Question
 

Have a mining customer that has a few crawler draglines. They are experiencing roller wear on #1 and #6 rollers (boogies for you Armour heads). I have 4 theories that could explain this. I'm wondering of I am missing anything?

http://forums.pelicanparts.com/uploa...1174503979.jpg

1) Boom Moment - produces downforce and additional stress on roller bearings 1 and 6 depending on direction

2) Track Slack - during movement increases stress on roller bearinsg 1 and 6 depending on direction

3) Contamination - during movement, dirt and dust presents to 1 and 6

4) Idle Arms - if not balenced, additional stress on 1 & 6


http://forums.pelicanparts.com/uploa...1174504245.jpg

What kind of load do you have on the boom?

How well sealed are the bearing units? In other words I assume that the middle bogies are as well sealed as 1 and 6, so what would change there other than the leading and trailing units being exposed to more debris when moving around.

If the boom load is high or excessive, #1 and #4 would be a place to start.

Also are they in a wet area? Water getting into bearings? Water getting into the area and then freezing?

All the bearings of the rollers are exposed partially to the elements - it is a coal mine so it is wet and dusty. As for loads...holy shyt it is in the thousands of foot tonne torque! You ever see a drag line crawler?

I'm not an engineer but my guess would be additional stress introduced at different points on the leading rollers. Are these two rollers beefed up as compared to the others?

RickM: No - they are the same as 2,3,4,5 but wear out at a 10X rate.

Some pics of some crawling draglines. Impressive:

http://forums.pelicanparts.com/uploa...1174505388.jpg http://forums.pelicanparts.com/uploa...1174505397.jpg http://forums.pelicanparts.com/uploa...1174505421.jpg

Man, that sounded like I'm being a shyt - not intended, sorry. :(

First thing I thought, contamination. Being that they are on the lead ends, they are in the prime spot to pick up crap before any of the other bearings

You need to talk to someone at CAT in the TTT (Track Type Tractor) division.

Center of lift transitioning from front and stopping and starting movement.......with the pivoting cab and the way operators usually run with the tracks pointing towards the lifting material and not the swing/dump area, the load and rocking action is greatest on the ends of the tracks.

If they side tracked more like the bottom right hand picture I believe some of the excessive wear would be mitigated but it has more inherent danger to it.

When they roll over rocks/bumps, the large end wheel rolls over the bump, then the first roller hits it hard. The gap between the rest of the center rollers is small enough to spread the load evenly unlike the big gap between the large lead wheels and the first small wheel.

Tim - that was a theory of one of the engineers. I think that has merit.

As with most failures, it is typically a combination of several factors.

Are rollers 2-5 set vertically higher than 1 or 6 and subsequently exposing 1 or 6 to greater load ?

The failure theory of #1 and #6 being the leading rollers and hence subject to the greatest impact/loading seems very plausible.

I think You'll find it a reverse cantilever issue. Heavy weight in the center makes the beam bow downward, and deflect the ends upwards. The most deflection and hence, misalignment, would be at the ends, rollers 1 and 6. Look at 2-5, if 3-4 have the least, I would suspect this.

My boss used to be an engineer at our lignite mine, I could ask him but I pissed him off so bad over the weekend that he hasn't talked to me since :o.

Yep, as Tim sez, you have a stress concentration situation.

Interesting. Here are my thoughts:

First, the carrier beam deflection will load the #1-6 rollers somewhat differently, but to get 10x wear on rollers 1 and 6 the deflection would have to be severe and oddly shaped. I doubt that is it.

Second, contamination is something all track wheels live with - why would 1 and 6 be that much worse? I'd rule that out also.

Third, the mounting arrangement of the idler arms and connection to the rollers is unknown. Don't know about interactions there.

Finally, track slack. This is one thing that definitely loads rollers 1 and 6 more than 2-5, but 10x the wear? My guess would be that it's track slack compounded by the difference in slack from the inside of the track to the outside of the track caused by uneven surfaces and crawler turns. This would not only add the additional radial load on the roller wheel but also add twist and thrust loads to the roller axles, carriers, and wheels. Placing strain gages on the roller carriers should tell if this is the case.

Haven't gotten to do this kind of stuff since engineering school!

Re: Engineering / Wear Question
 

this looks like a job for...! ;)

I think Tim is right. This is my thought exactly. Im at RPI for engineering but am no expert yet.

Good news, my boss talked to me before I went home today :). I feel like I'm dealing with my wife having a little silent treatment tantrum.

Anyway, when you receive the bearings are they completely demolished? If not, I would think you could rule out contamination or overload pretty quick. Don't they have different damage signatures?

Since 1 & 6 take more load then 2-5, overloading seems a good choice, but I think a closer look at the bearing surface and subsurface would tell more.

Ah, a Troilet!